Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,953,441 to Setlak and assigned to the assignee of the present invention, the entire contents of which are herein incorporated by reference. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate.
U.S. Pat. No. 6,289,114 to Mainguet, which is assigned to the assignee of the present invention and is incorporated in its entirety by reference, discloses a fingerprint sensor that includes a finger sensing integrated circuit (IC). The finger sensing IC includes a layer of piezoelectric or pyroelectric material placed between upper and lower electrodes to provide electric signals representative of an image of the ridges and valleys of the fingerprint.
A particularly advantageous approach to multi-biometric fingerprint sensing is disclosed in U.S. Pat. No. 7,361,919 to Setlak, which is assigned to the assignee of the present invention and is incorporated in its entirety by reference. The Setlak patent discloses a multi-biometric finger sensor sensing different biometric characteristics of a user's finger that have different matching selectivities.
A fingerprint sensor may be particularly advantageous for verification and/or authentication in an electronic device, and more particularly, a portable device, for example. Such a fingerprint sensor may be carried by the housing of a portable electronic device, for example, and may be sized to sense a fingerprint from a single-finger. For example, the AES3400 sensor from AuthenTec, Inc. of Melbourne, Fla., the assignee of the present invention, is widely used in a variety of notebooks, desktops and PC peripherals. Other fingerprint sensors, for example, the AES850, also from AuthenTec, Inc. of Melbourne, Fla., is a multi-function smart sensor that expands touch-based functionality of touchscreen and QWERTY smartphones with a reduced impact on sensor performance or durability. Thus, a fingerprint sensor may be particularly advantageous for providing more convenient access to the electronic device without a password, for example, and, more particularly, without having to type the password, which is often time consuming. A fingerprint sensor may also be particularly advantageous for starting one or more applications on the electronic device.
U.S. Patent Application Publication No. 2011/0175703 to Benkley, III discloses an electronic imager using an impedance sensor grid array mounted on or about a switch. More particularly, Benkley, III discloses a switch being incorporated into a sensor assembly that allows integration of sensor operations, such as, fingerprint sensor operations. A fingerprint sensor can be used for authentication while being used together with a power switch or navigation selection switch. The authentication may be used to access the device entirely or access different levels of information.
U.S. Patent Application Publication No. 2009/0083850 to Fadell et al. discloses an embedded authentication system in an electronic device. More particularly, Fadell et al. discloses authenticating a user via a fingerprint to provide access to resources or content that was previously not available. The electronic device may allow a user to authenticate for a particular amount of time for accessing restricted resources.
U.S. Pat. No. 7,809,168 to Abiko et al. discloses a biometric information input device. More particularly, Abiko et al. discloses a movement direction detection means for detecting a movement direction of a finger with respect to the fingerprint sensor, based on partial fingerprint images collected by the fingerprint sensor.
Moreover, while a fingerprint sensor used in an electronic device may be particularly advantageous for authentication, navigation, etc., these finger sensors generally require the user's finger to be placed in a very close proximity to the array of finger sensing pixels. The need for close proximity to the user's finger typically makes the mechanical packaging and the integration of a fingerprint sensor into the electronic device more difficult and more costly.
Some approaches to address packaging of an electronic device include a special molded package with an opening in the molding allowing the finger a close approach to the finger sensing array. Specialized packaging increases the cost of these sensors.
The desire for the user's finger to be close to the array of finger sensing pixels may limit the thickness of the material that can be placed over the array of finger sensing pixels, which may increasingly restrict the use of both protective and cosmetic coatings over the array area. Mechanically integrating these sensors into their host devices typically requires that the finger sensor project through a hole in the electronic device's case, so that the array of finger sensing pixels can be located about flush with the external surface of the case.
However, a negative aspect of these mounting arrangements may include increased difficulty and cost to seal the opening for the finger sensor in the electronic device case or housing against the ingress of moisture, dust, and other contaminants. Additionally, the opening in the case or housing with the finger sensor protruding may be cosmetically unacceptable to the intended appearance of the electronic device, and mounting the finger sensor in an opening in the case may be difficult and costly in some devices.
It may be desirable to extend the range of electric field based finger sensors so that they can image fingers through significantly thicker dielectric materials such as molded plastic structures. Using an increased thickness material layer over the array of finger sensing pixels may result in increased power consumption. More particularly, an increased thickness material layer generally requires a greater drive voltage to be driven into the user's finger. The greater distance from the array of finger sensing pixels and the increased drive voltage may result in increased noise of a finger image, which may be undesirable for authentication, for example.